Process of and apparatus for oxidizing metal sulphides and making sulphur dioxide



June 30, 1931. H. FREEMAN 1,812,397

PROCESS OF AND APPARATUS FOR OXIDIZING METAL SULPHIDES AND MAKING SULPHUR DIOXIDE Filed Jan. 1'7, 1929 C fill? a sup/110E 4 9 w? A/RXG/IS L l g //We/7/0/- fibrace flee/nan Patented. June 30, 1931 Umran STATES PATENT OFFICE.

BOB-AGE rnmnmir, or snawmrenr runs, aunanc, CANADA, assronon 'ro m aunrmnn anscsancn conrona'rron alarm), or nonramn, owns, a conronanou OF CANADA rnocnss or m arraaa'rus FOR oxrnrzme METAL sunrnnms AND ammo SULPHUR DIOXIDE Application filed January 17, 1929. Serial No.

l This invention relates to process of and apparatus for oxidizing metal sulphides, and the principal objects of the invention are the production of sulphur d oxide of sulfi- 5 cient purity for the manufacture of sul hurous and sulphuric acids and, if desire the production of a dustless, solid, smtered residue. I

A further object of the invention is the pro- 19 vision of a novel process of oxidation and a novel type of furnace adaptable to a variety of uses.

An important feature of the invention is that the rate of air input to the combustion chamber is so proportioned to the dimensions of the latter that the sulphide particles are kept in suspension in the uprising air current for suficient length of time to substantially complete theircombustion before reach- 20 ing the bottom of the furnace where the formed oxide is removed. Sulphur which may remain in the particles may be removed from the sintered residue by passing air through it.

Another feature of the invention 1s that the sulphide particles are rapidly heated to a state of incipient fusion and, in this state, are inflated by evolution-of gas therefrom to provide a very large surface for oxidation and may eventually be collected in the form of-a highly'poro'us solid sintered mass.

A further feature of the invention is that the oxidation is accomplished at high temperature and without use of fuel other than the sulphide itself and that an excess of heat is available for recovery and utilization.

Incarrying out the invention, d finely dividedmetal sulphide (for examp e, such as will pass through a mesh screen) is injected, by means of a current of air insufiicient in amount for complete combustion of the sulphide into a combustion chamber heated to a temperature at which the sulphide will ignite in the air. The rate of sulphide feed is in such relation to the dimensions of oss uponthose sulphides which yield oxides withv high melting temperatures, notably :those of .iron and zinc, but with suitable the combustion cha'mberthat the velocity of -the ases resulting from. combustion of the j sulp ide will be about five to ten feet per second. The burning sulphide meets acountercurrent of air or gas mixture containing corrode a boiler. Owing to the high temperam REISSUED free oxygen in amount sufiicient to complete the oxidation of the sulphide. Owing to the low velocity of the gaseous combustion products, the burning sulphide will fall but is impeded by the countercurrent of air sufficiently to allow substantially complete combustion before the particles reach the bottom of the chamber, where they are collected in running water or collected on a travelling grate in the form of a sintered mass and are transported out of the combustion chamber by the grate. When a travelling grate is used the air necessary to complete oxidation is first drawn or blown through the sintered mass after it is removed from the furnace, thus serving the 4% triple purpose of burning any sulphur which has not been consumed in the furnace, cooling the sintered mass and preheatin the air. This preheated air carryinga sma l proportion of sulphur dioxide is then passed mto the combustion chamber through the grate. The finely divided sulphide exposed to high temperature burns uickly and with such evolution of heat that t e esca ing gaseous products of combustion ma be advantageously passed through a steam oiler both to cool the gas and to recover the heat in the steam which Wlll be generated. The high temperature ensures freedom from acid gases which would ture prevailing in the combustion chamber, oxidation of the finely divided sulphide commences almost instantly on entrance into the combustion chamber and the sulphide loses, some of its sulphur content, thereby becomin 35 more readily fusible. The small particles 0 sulphide in a state of incipient fusionare apparently inflated, by the evolution of gases therefrom, into small hollow globular bodie or bubbles, which settle slowly through the rising air and gas and collect on the grate to form a solid but very porous sintered mass through which the incoming air flows without difiiculty.

This process operates with greatest sucregulation of the rates of sulphideand' air feeds, the process may be applied also to 133 which are admirably suited to the process without previous treatment as is required in other methods of roasting.

The form of apparatus now' preferred is shown more or less diagrammatlcally in the accompanying drawing, but it will be understood that the invention is not confined to any or all of the details of the apparatus 1 lustrated, as numerous changes may be made.

Referring more particularly to the drawing, 11 designates a gas-tight furnace shell, preferably of metal, having a refractory lining 12. At the bottom of the furnace is a travelling grate 13, shown as of the endless belt type, but which may be of rotary or any other suitable type. Close to the furnace a suction box 14 is provided beneath the out coming grate and is connectedt'o a blower 15, which discharges into an air chamber 16 beneath the furnace and below the grate. Air and finely divided dry sulphide are passed downwardly into the top of the furnace through a conduit 17.. A gas outlet 18 is provided at the top of the furnace.

The operation of the process and apparatus, broadly speaking, is that the finely divided material is fed into the furnace and forms a flame whence it falls onto the travelling grate, where it is further burned with preheated air passed upwardly through the grate. The travelling grate removes the solid combustion residue from the furnace and the air necessary for combustion is preheated by being drawn through the grate and hot solid combustion residue thereon at a point outside the furnace. Material which has secaped unburned from the furnace is burned'on the grate outside the furnace and the heat and.

gases of combustion are introduced into thev furnace with the air. The solid residue is also cooled. The process generally may also extend to introducing with the fuel air insufficient for its complete combustion.

.In greater detail, the operation of the process and of the apparatus depicted is as follows ;Dry, finely divided metal sulphide, such as a flotation concentrate or finely crushed iron pyrites, is injected with less air than required for its complete oxidation (termed primary air) downwardly intothe highly heated furnace slowly, while the sulphide ignites and falls burning, onto the h travelling gratel3. While falling, the particles are heated to a state of incipient fusion and, in this state, are inflated by the gas evolving from them and present very large surface for oxidation, relative to the volume of the particles.

"The partially oxidized sulphide particles in the sticky state of incipient fusion collect on the grate in the form of an extremely porous or spongy cake, which is quite pervious to the air (termed secondary air) pass ing up through the grate. The greater part of the oxidation occurs before the sulphide reaches the grate and the sintered mass leav-' ing the furnace is to 99% oxidized. The blower 15 draws air (termed tertiary air) through the sintered mass on the grate immediately after it leaves the furnace. The relatively large amount of air substantially completes the oxidation, recovers a lar e proportion of the heat of the sinter ca e and preheats the air entering the furnace.

The sulphur content of the sinter cake may thus be reduced as low as .0170. The preheated entering air (carrying a small percentage of sulphur dioxide) oxidizes the sulphide on the grate as previously stated and then passes upwardly through the furnace,

oxidizing the falling particles of sulphide and reacting with any vaporous elemental sulphur which has distilled out of the sullphide on its initial exposure to the furnace eat. With properly adjusted air supplies, the gas escaping from the furnace is substantially all sulphur dioxide and nitrogen.

Owing to treating the sulphides in finely divided state and at high temperature, the oxidation is very rapid and there is little time for loss of heat, so that considerable of the heat of combustion may be recovered, which may be done by passing. the hot gases through a steam boiler. This also rapidly cools the gas.

It will be seen that the counter current air may pass once or twice through the hot pervious sinter cake and, obviously, the number oxygen and whichwill not react undesirably With the sulphide or formed oxide may be substituted for air. In the following claims, the term air? is to be construed as including such gas mixtures.

The preferred temperature of operation will vary according to the sulphide treated and may be stated to lie above the ignition temperature of the sulphide and below-the temperature at which the material collecting on the grate is so far fused as to be diflicultly pervious to the entering air. 7

While ;the grate preferably travels continuously at low lineal speed, it may have an integrating movement. v

While the'sulphide introducing current of gas has been stated to be air, it will be understood that a nonoxidizinggas may be substituted and all the oxidizing effect obtained from a counter current of oxidizing gas, or,

- ratelyfrom the two countercurrent streams.

Having thus described my invention, what I claim is i 1. Aprocess of oxidizing meta-l sulphides which comprises introducing the sulphide in finely divided form into a preheated combustion chamber with an amount of air insufficient for complete oxidation, and introducin a countercurrentof air in amount sufficient to substantially complete the oxidation.

A process according to claim -1, in which the-'combustion chamber is maintained at such temperature that the sulphide particles are semi-fused and inflated by evolution of gas therefrom and collect in a spongy solid mass readily pervious to the passage of air.

3. A process according to claim 1, in which the sulphide is introduced downwardly into the top of the combustion chamber.

l. A process according to claim 1, in which the sulphide in a state of incipient fusion and inflated by evolution of gas therefrom is collected in a spongy mass through which the counter current of air is introduced into the combustion chamber.

5. A process according to claim 1, in which the counter current of air is preheated and oxidation of the sulphide completed by passing the air in contact with the substantially completely oxidized sulphide at a point outside the combustion chamber.

6. A process of oxidizing metal sulphides,

which comprises introducing the sulphide in finely divided state with an amount of air insufficient for complete oxidation of the sulphide into a combustion chamber heated to a temperature above the ignition temperature of the sulphide and below the tempera ture at which the sulphide would fuse to a' mass impervious to air, collecting the partially oxidized sulphide in "a layer pervious to air, passinga' secondary supply of. air, in ount sufficient to substantially complete oxidation of the sulphide, through the pervious layer of sulphide into the combustion chamber and countercurrent to the entering sulphide, removing substantially completely oxidized sulphide from the combustion eliamber and completing the oxidation ofithj sulphide, cooling the same, and preheating the secondary air supply by assing the air through the-withdrawn sulp hide prior to ingoducing said air into the combustion chamr. 7 A process according to claim 1, in which the combustion chamber is maintained at a temperature between the ignition temperature of the sulphide and the temperature at which-the partially oxidized sulphide would fuse and collect in a mass impervious to. air.

8. A- process of oxidizing metal sulphides, which comprises passing a relatively large proportion of air downwardlyv through a hot spongy layer of nearly completely oxidized sulphide, passing the resulting heated mixture' of gas and air upwardly through a hot pervious layer of less completely oxidized sulphide into a countercurrent of finely divided substantially unoxidized sulphide and air enterin a combustion chamber heated. above the ignition temperature of the sulphide.

9. A process according to claim 1, in which the partially oxidized sulphide is collected in a pervious layer and the countercurrent air passed a plurality of times through said layer prior to entry of said air'into the combustion chamber.

10. A process according toclaim 1, in which substantially completel oxidized sulphide is continuously remove in a pervious layer, from the combustion chamber and the countercurrent air introduced through such moving layer into the combustion chamber.

11. ll. process according to claim 1, in which partially oxidized sulphide is collected in a pervious layer and the countercurrent air passed a plurality of times through such layer, in suchwise that the air contacts successively with progressively hotter and progressively less oxidized portions of the layer. 12. A process of oxidizing metal sulphides and producing sulphur dioxide therefrom, which comprises introducing the sulphides in finely divided form into the upper end of a heated combustion zone through which the sulphides will gravitate substantially vertically downward, and introducing into the lower end of said zone in vertically upward direction a current of air for combustion of the sulphides and so regulating the amount and velocity of the air relatively to the introduction of sulphide and the dimensions of the combustion zone that the gravitation of the sulphide particles is retarded substantially without lateral deflection of the particles from their downward path until combustion is substantially complete and the particles "with one another, and heating the sulphide particles whlle moving countercurrent to the fair etam the ignitiontemperature of the 1 pgrticles the amount of velocity of the air I whic ing such as to maintain the particles in susgravitation for such lengthof time as will air supp ensure substantially complete oxidation of the sulphide, and heating the sulphide while passing countercurrent to the air to at least the temperature of ignition of the sulphide the amount of velocity of the air being such as to maintain the particles in suspension until they attain to a sticky state ofincipient fusion.

' 15. A and pro ucing sulphur dioxide therefrom, which com rises creating in a confined space a flame of ely divided metal sulphide with air insufiicient in amount for complete combustion of the sulphide, introducing into saldv space a secondary supply of air in amount suflicient to complete combustion of the sulphide and directing the sulphide and primary y countercurrent to the secondary air supply.

16. A process of oxidizing metal sulphides and 1p whic a flame of ely divided metal sulphide with air insufficient in amount for complete com bustion of the sulphide, introducing into said space asecondary supply of air in amount sufficient to complete combustion of the sulphide, directing the sulphide and primary air supply countercurrent to the secondary a1r supply, maintaining the temperature such that the sulphide will be heated to a state of incipient fusion, collecting the sulphides while in such state of incipient fusion in a layer pervious to fair, and causing the secondary air in process of introduction into said space to pass through said pervious layer of sulphide.

' 17. A process of oxidizing metal sulphides,

which comprises introducing the sulphides in finely divided form into an oxidizing atmosphere in a combustion zone heated to at least the ignition temperature of the sulphides,

" and maintaining the sulphides in suspension in said atmosphere until substantially completely oxidized and heated to a sticky state of incipient fusion by establishing counter currents of gas in said combustion zone in such direction and at such velocity that gravitation of the sulphide particles is retarded substantially without lateral deflection'of the particles from their normal downward path due to the action of gravity.

.atmosp process ofoxidizing metal sulphides roducing sulphur dioxide therefrom, com rises creatmg 1n a confined space- 18. A process of oxidizing metal sulphides which comprises passing a current of as an 1 a stream of the sulphide in finely 'vided state in opposite directions in an oxidizing atmosphere whereby the passage of the particles 1s retarded and the articles maintained in contact with the oxi izing atmosphere a sufficient len h of time for substantially complete com ustion and the attainment of a sticky state of incipient fusion, and heatin the sulphide in contact with the oxidizing ere to at least the ignition temperature of the sulphide.

19. Apparatus for the oxidation of metal sulphides, which comprises a combustion chamber, a travelling grate at the bottom of said chamber, a suction box below the grate outside the combustion chamber, a blower connected to the suction box and to the combustion chamber below the grate to draw air through the rate and material thereon into the suction ox and to discharge the air through the grate and material thereon at another point into the combustion chamber, and means to feed sulphide into the combustion chamber.

20. Apparatus for oxidizing metal sulphides comprising a combustion chamber,

means to feed finely divided sulphide and air into said chamber, means to collect partly oxidized sulphide in a la er and to remove the same from the cham er, and means to pass air through the layer of sulphide.

21. A furnace comprising a combustion chamber, a travelling grate arrangedto support fuel in the furnace and to withdraw fuel residue or partly burned fuel from the furnace, and means to pass air a plurality of times through fuel on the grate and into the combustion chamber, the means being such that the first passage of air is through fuel withdrawn from the furnace.

22. A process of oxidizing metal sulphides and producing sulphur dioxide therefrom, which comprises introducing the sulphides in finely divided form together with insuflicient air for complete combustion into the upper end of a heated combustion zone through which the sulphides will gravitate substantially vertically downward, and introducing into the lower end of said zone in vertically upward direction a current of air suflicient to complete combustion of the sulphides, and so regulating the amount and velocity of the air relatively to the introduction of sulphide and the dimensions of the combustion zone that the gravitation of the sulphide particles is retarded substantially without lateral deflection of the particles from their downward path until combustion is substantially complete.

23. A process of oxidizing metal sul hides, which comprises introducing the sulp ide in finely divided form into an oxidizing atmosleast the ignition temperature of the sul phide, collecting the solid products of combustion at the bottom of the chamber and passing a stream of air through the solid products of combustion, whereby unburned sulphide in said solid product is oxidized and the air preheated, into the combustion chamber and countercurrent to the sulphide, the I amount and Velocity of the air being such as to maintain the sulphide in suspension in the oxidizing atmosphere until substantially completely oxidized.

In witness whereof, I have hereunto set In hand.

y HORACE FREEMAN.

zing metal sulphides 

